Regulation of Saliva - Podcast Version TeachMePhysiology 0:00 / 0:00 1x 0.25x 0.5x 0.75x 1x 1.25x 1.5x 1.75x 2x The human body produces approximately 1.5 litres of saliva each day. Saliva plays a vital role in lubricating food, aiding digestion, and protecting the oral environment. Salivary production and composition are under neural control by the parasympathetic and sympathetic divisions of the autonomic nervous system. In this article, we will discuss the regulation of salivary secretion and its clinical correlations. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Production of Saliva Saliva is produced by the major salivary glands of the body: the parotid (near the ears), submandibular (under the jaw), and sublingual glands (under the tongue). Within these glands, acinar cells secrete the primary fluid component of saliva, while duct cells modify its composition as it passes through the ductal system. Further detail on the composition of saliva and mechanisms underlying this can be found here. Adobe Stock, Licensed to TeachMeSeries Ltd Fig 1Diagram showing the location of the major salivary glands. Autonomic Control The salivary glands receive input from both sympathetic and parasympathetic fibres of the autonomic nervous system. Both arms regulate saliva volume and composition, but parasympathetic stimulation predominantly determines flow rate. Sympathetic Innervation Sympathetic fibres arise from the superior cervical ganglion and release noradrenaline, which acts on alpha- and beta-adrenergic receptors. Stimulation of the adrenergic receptors causes: Decreased production of saliva by acinar cells. Increased protein (enzyme) secretion. Decreased blood flow to the salivary glands. Overall, sympathetic stimulation produces a low-volume, enzyme-rich saliva. Sympathetic innervation varies between glands, and overall, it plays a less dominant role than parasympathetic input in regulating total saliva production. Parasympathetic Innervation Parasympathetic outflow is coordinated by the salivatory nuclei in the medulla. Fibres travel via the facial (CN VII) and glossopharyngeal (CN IX) nerves. Afferent signals from the oral cavity, tongue, nose and conditioned reflexes are integrated centrally within the brain causing parasympathetic stimulation in the presence of food. Parasympathetic fibres release acetylcholine (ACh) at M3 muscarinic receptors, causing: Increased production of saliva by acinar cells. Increased secretion of HCO3– by ductal cells. Increased blood flow to the salivary glands – via the action of co-transmitters, such as vasoactive intestinal peptide (VIP). Contraction of myoepithelial cells to expel saliva faster Overall, parasympathetic stimulation produces a high-volume, watery saliva suitable for lubrication and digestion. Created in BioRender Fig 2Path of parasympathetic fibres to the salivary glands. Autonomic fibres travel with other cranial nerves such as CN IX, as pictured. Clinical Relevance Sialorrhoea Sialorrhoea refers to excessive drooling due to an inability to adequately control saliva within the oral cavity. It may arise via two principal mechanisms. Impaired swallowing – resulting in pooling of saliva within the mouth. This is most commonly associated with neuromuscular or neurodegenerative conditions such as cerebral palsy, Parkinson’s disease or motor neurone disease. Increased salivary secretion – which is most frequently medication-induced. This is often observed in patients receiving anti-cholinesterase therapy, such as those being treated for Alzheimer’s disease or myasthenia gravis. Management depends on the underlying cause and is primarily focused on addressing reversible factors. This may involve adjusting or discontinuing causative medications where appropriate. Behavioural strategies can also be employed to improve saliva clearance and reduce pooling. In more severe or refractory cases, anticholinergic medications may be used to reduce salivary secretion; however, their use is often limited by systemic side effects (dry mouth, blurred vision, constipation, urinary retention). If conservative measures fail, more invasive options such as botulinum toxin injections, radiotherapy or surgical intervention may be considered. Do you think you’re ready? Take the quiz below Pro Feature - Quiz Regulation of Saliva Question 1 of 3 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/3 More Questions Available Upgrade to TeachMePhysiology Pro Challenge yourself with over 2100 multiple-choice questions to reinforce learning Learn More Rate This Article